A variety of single piece lightweight respirators and masks are available in the form of facepieces which cover the nose and mouth and provide breathing protection from dust and particulate matter. Such single piece disposable dust respirators, however, are unable to exclude undesirable vapors and gases. In order to filter or treat organic vapors and gases, more complex respirators and masks are required incorporating cartridges or chambers confining an active filter material through which breathing air passes for filtering or treatment. Such full mask and half-mask facepieces and respirators are generally more cumbersome and heavier in weight, with more complex construction required for safely confining and containing the active filter material in the cartridge through which breathing air passes.
The conventional cartridge type filter or respirator uses a cartridge of porous or perforated end walls containing relatively large mesh granulated or pelletized activated carbon. The end walls typically include a porous membrane and a perforated structural screen. The relatively large mesh size of the granules or pellets packed between the porous end walls of the cartridge is selected to afford low pressure drop restriction across the cartridge particularly in respirator applications to minimize resistance to the breathing air flow. Minimizing the pressure drop and resistance to flow by selection of large size granules or pellets, however, reduces the surface area exposure of the active surface material comprising the granules or pellets. Surface area exposure of the active surface material such as activated carbon or charcoal is optimized using active surface particle powder of powder mesh sizes, for example, Tyler or U.S. Standard Screen Mesh Size 200 and smaller and preferably fine powder Tyler or U.S. Standard Screen Mesh Size of at least 325 and smaller. Applications for packed powder and fine powder filter cartridges, however, are generally limited to filtering liquid fluids and to liquid purification because the high pressure drop across packed powder is unsuitable for vapor and gas filtering and breathing applications.
The use of high exposure surface area powder and fine powder active surface material such as activated carbon and charcoal powders of mesh size finer than 200 mesh and preferably finer than 325 mesh have not been available for vapor and gas filtering applications. The powder material must be securely confined to eliminate breathing hazards or release of the powder. Such cartridge elements exhibit high resistance to vapor and gas flow. As a result no active filter material or medium is available which combines the advantages of the high exposure surface area of active surface powders and fine powders with the low resistance to flow and low pressure drop of packed granules and pellets of larger mesh size.
Furthermore, even for liquid filtering applications, a disadvantage of present methods is that fine powder may be released into the liquid, or the powder is intentionally mixed with the liquid and extended settling time or contrifugation is thereafter required.